A child on a march to support Article 12 of the UN Convention on the Rights of the Child which protects children from all forms of physical punishment. Photograph: Rebecca Naden/PA

A third of adults think slapping children as young as six years old is a low-risk form of punishment, with almost half of older people believing parents can hit children with no fear of them causing harm or distress.

New research published today from the Children's Society reveals that just 14% of adults – one in seven – think slapping children and young people is an unacceptable form of punishment.

The Children's Society is now calling on the government to make it illegal to strike children with an open hand. The UK is one of five EU countries currently resisting an all-out ban on slapping, a stance that has led to criticism from human rights groups on the grounds that it is contravening article 19 of the UN convention of the rights of the child.

"Physical violence is something children definitely need to be protected from," said Bob Reitemeier, the chief executive of the Children's Society. "Our survey revealed a worrying lack of concern by one third of people surveyed about parents slapping children.

"Children are the only group of people in this country who can be legally hit on a regular basis by others with little protection in law."

The survey of more than 2,000 adults across the UK was part of a major research project on safeguarding young people being undertaken by the Children's Society, the NSPCC and the University of York.

The research revealed that 32% of respondents said slapping children aged between six and 15 was a form of punishment that carried little risk of causing emotional or physical distress on the part of the child.

Among older adults, however, there was a hardening of views. Some 46% of respondents aged over 65 said slapping children was completely acceptable, compared with 27% of those aged 18 to 24.

When asked what form of behaviour by a parent would trigger their concern as a passerby, slapping came lowest on respondents' lists of priorities, below seeing a parent call their child "stupid", refusing to take them to a dentist or knowing where they were at 9pm on a summer evening.

Adults became less tolerant of physical punishment if they lived with children. More than 40% of respondents who shared their home with a child said it was an unacceptable form of retribution, compared with 29% of those who did not.

Surprisingly, Reitemeier said, those polled believed that the older the children subjected to physical punishment were, the higher the risk they faced of suffering emotional or physical abuse. "This finding may indicate a belief that physical punishment is more psychologically damaging to older children," he said.